C and Si both have the same lattice structure, having 4 bonding electrons in each. However, C is an insulator

Question

C and Si both have the same lattice structure, having 4 bonding electrons in each. However, C is an insulator whereas Si is an intrinsic semiconductor. This is because:

Accepted Answer

1. **Electronic Configuration:** Carbon (atomic number 6) has the electronic configuration $1s^2 2s^2 2p^2$, meaning its 4 valence (bonding) electrons are in the second principal quantum shell ($n=2$). Silicon (atomic number 14) has the configuration $1s^2 2s^2 2p^6 3s^2 3p^2$, so its 4 valence electrons are in the third shell ($n=3$).
2. **Band Gap:** Because the valence electrons in carbon are in the $n=2$ orbit, they are much closer to the nucleus and more tightly bound than the $n=3$ electrons in silicon. 
3. **Conclusion:** This strong binding in carbon results in a very large energy gap (band gap $\approx 5.4	ext{ eV}$) between the valence band and the conduction band, making diamond (carbon) an insulator. In contrast, the electrons in silicon are farther from the nucleus, resulting in a smaller band gap ($\approx 1.1	ext{ eV}$), which allows it to act as an intrinsic semiconductor at room temperature.

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